Magnesium

Table of Contents

Magnesium (Mg) is an element belonging to the alkaline earth metal group. It participates in over 300 metabolic reactions, is crucial for life and health and is

Magnesium

Age

Recommended Dietary Allowance (mg)

Tolerable Upper Intake Level of Dietary Supplements (mg)

Children 0–6 mos.

30 (AI)

Not established

Children 7–12 mos.

75 (AI)

Not established

Children 1–3 yrs.

80

65

Children 4–8 yrs.

130

110

Children 9–13 yrs.

240

350

Boys 14–18 yrs.

410

350

Girls 14–18 yrs.

360

350

Men 19–30 yrs.

400

350

Women 19–30 yrs.

310

350

Men 31≤ yrs.

420

350

Women 31≤ yrs.

320

350

Pregnant women 18≥ yrs.

400

350

Pregnant women 19–30 yrs.

350

350

Pregnant women 31≤ yrs.

360

350

Breastfeeding women 18≥ yrs.

360

350

Breastfeeding women 19–30 yrs.

310

350

Breastfeeding women 31≤ yrs.

320

350

Food

Magnesium (mg)

Cereal, 100% bran, ½ cup

129

Oat bran, ½ cup, dry

96

Halibut, cooked, 3 oz.

90

Almonds, roasted, 1 oz.

80

Cashew nuts, roasted, 1 oz.

75

Spinach, cooked, ½ cup

75

Swiss chard, cooked, ½ cup

75

Beans, lima, cooked, ½ cup

63

Shredded wheat, 2 biscuits

54

Peanuts, roasted, 1 oz.

50

Black-eyed peas, cooked, ½ cup

43

Brown rice, cooked, ½ cup

40

Beans, pinto, cooked, ½ cup

35

AI = Adequate Intake

mg = milligram

(Illustration by GGS Information Services/Thomson Gale.)

the fourth most common mineral in the body. In the body, it forms ions that have an electric charge of +2. Humans must meet their needs for magnesium from their diet. Magnesium is found mainly in plants and in some drinking water.

Magnesium is necessary for many cellular reactions critical to maintaining life. It plays a role in:

strengthening bones

synthesizing new deoxyribonucleic acid (DNA; genetic >material)

synthesizing proteins

muscle contraction

KEY TERMS

Dietary supplement—A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individuals diet with the expectation that it will improve health

Diuretic —A substance that removes water from the body by increasing urine production

Magnesium is in chlorophyll, the pigment that makes plants green. Humans absorb magnesium from food as it passes through the small intestine. The kidneys normally regulate how much magnesium is in the blood, and any excess magnesium is excreted in urine. Magnesium levels can be measured with a blood test.

When magnesium dissolves in body fluids, it becomes an electrolyte. Electrolytes are ions that have an electric charge. Magnesium is a cation, or positively charged ion, with an electric charge of +2, meaning it has lost two of its negatively charged elections. Other important electrolytes in the body are sodium (Na+ ), potassium (K+), calcium (Ca 2+), and the negatively charged ions chloride (Cl-), phosphate (HPO4 2-), bicarbonate (HCO3-), and Sulfate (SO4 2-). Multiple electrolytes are involved in most metabolic reactions. These electrolytes are not evenly distributed within the body, and their electric charge and uneven distribution are what allow many chemical reactions to occur. About 50-60% of the 25 grams of magnesium in an adult’s body, is in the bones. About 25% is in muscle cells, 6–7% in other cells, and less than 1% outside cells (e.g. in extracellular fluid or in blood serum).

Magnesium is involved in many reactions. One of the most important is in synthesizing adenosine tri-phosphate (ATP), the molecule that supplies most of the energy to drive cellular metabolism. Magnesium is also required to create new DNA, Ribonucleic acid (RNA), and proteins. The electrical charge of the magnesium ion is important in regulating the transmission of nerve impulses, muscle contraction, and the movement of nutrients and other electrolytes in and out of cells. Magnesium also has an effect on the way calcium is deposited in bones. It makes bone structurally more dense and stronger.

Normal magnesium requirements

The IOM has not set RDAs for magnesium in children under one year old because of incomplete scientific information. Instead, it has set AI levels for this age group. The RDAs for magnesium are the amount that has been determined to prevent deficiency. However, based on recent findings about the relationship between magnesium, diabetes, and cardiovascular disease, there is some debate over whether this represents the optimum amount for health. RDAs and ULs for magnesium are measured in milligrams (mg). There are no ULs for magnesium that is obtained from food and water. All magnesium ULs apply to dietary supplements only.

The following list gives the daily RDAs and IAs and ULs for magnesium for healthy individuals as established by the IOM.

children birth–6 months: AI 30 mg; UL not established; All magnesium should come from breast milk, fortified formula, or food.

children 7–12 months: AI 75 mg; UL not established; All magnesium should come from breast milk, fortified formula, or food.

children 1–3 years: RDA 80 mg; UL 65 mg

children 4–8 years: RDA 130 mg; UL 110 mg

children 9–13 years: RDA 240 mg; UL 350 mg

boys 14–18 years: RDA 410 mg; UL 350 mg

girls 14–18 years: RDA 360 mg; UL 350 mg

men 19–30 years: RDA 400 mg; UL 350 mg

women 19–30 years: RDA 310 mg; UL 350 mg

men age 31 and older: RDA 420 mg; UL 350 mg

women age 31 and older: RDA 320 mg; UL 350 mg

pregnant women 18 years and younger: RDA 400 mg; UL 350 mg

pregnantwomen 19–30years: RDA350mg;UL350mg

pregnant women 31 years and older: RDA 360 mg; UL 350 mg

breastfeeding women 18 years and younger: RDA 360 mg; UL 350 mg

breastfeeding women 19–30 years: RDA 310 mg; UL 350

breastfeeding women 31 years and older: RDA 320 mg; UL 350 mg

Sources of magnesium

Chlorophyll, the pigment that makes plants green, contains magnesium. Good natural sources of magnesium include dark green vegetables such as spinach and Swiss chard. Other vegetables high in magnesium are lima beans, black-eyed peas, almonds, cashew nuts, and peanuts. Whole grains contain a lot of magnesium, but processing removes most of it. Therefore brown rice is a good source of magnesium, but white rice is not. Whole wheat flour has more magnesium than white flour, and wheat bran and oat bran have more than either type of flour. Some water that is high in minerals (hard water) has a significant amount of magnesium; the amount varies widely depending on location. Magnesium is also found in many multivitamins and is available as a single-ingredient supplement. The amount of magnesium available to the body from dietary supplements varies depending on the molecule in which magnesium is found. Common forms of magnesium in dietary supplements include magn! esium oxide, magnesium gluconate, magnesium citrate, and magnesium aspartate. Some antacids contain a significant amount of magnesium hydroxide. The best way to get an adequate amount of magnesium is to eat a healthy diet high in green vegetables and whole grains.

The following list gives the approximate magnesium content for some common foods:

100% bran cereal, ½ cup: 129 mg

oat bran, ½ cup dry: 96 mg

shredded wheat, 2 biscuits: 54 mg

halibut, cooked 3 ounces: 90 mg

almonds, roasted, 1 ounce: 80 mg

cashew nuts, roasted, 1 ounce:75 mg

peanuts, roasted, 1 ounce: 50 mg

spinach, cooked, ½ cup: 75 mg

Swiss chard, cooked, ½ cup: 75 mg

lima beans, cooked, ½ cup: 63 mg

black-eyed peas, cooked, ½ cup: 43 mg

pinto beans, cooked, ½ cup: 35 mg

brown rice, cooked, ½ cup: 40 mg

Magnesium excess and deficiency

Hypomagnesemia, or low levels of magnesium are estimated to occur in about 2 of the American population, in 1,020 of hospitalized patients, and in up to 60 of patients in intensive care. Anywhere between 30 and 80 of people with alcoholism have hypomagnesemia, as do about one-fourth of people with diabetes.

Magnesium deficiency can be caused either by insufficient intake or excessive excretion of magnesium. Causes of insufficient intake include digestive disorders that interfere with the absorption of magnesium (e.g. Crohns disease, celiac disease, inflammatory bowel syndrome), malnutrition with a limited diet of green vegetables, alcoholism (alcohol is substituted for food), and anorexia nervosa (self-starvation). Some causes of excessive excretion of magnesium include kidney failure, diabetes, use of some diuretic drugs, and some hormone disorders of the parathyroid gland.

The kidneys are the main regulator of magnesium. People with kidney disease should not take magnesium supplements.

Pregnant women should discuss their magnesium needs with their healthcare provider. Many pregnant women have low levels of magnesium but should use supplements only under medical supervision. Low magnesium levels are thought to contribute to preeclampsia and eclampsia and possibly to increase the risk of early labor.

People undergoing surgery should tell their anesthesiologist if they are taking magnesium supplements, antacids, or laxatives because magnesium increases the muscle-relaxing effects of certain anesthetics.

Certain drugs and conditions can cause an excessive loss of magnesium. These include:

cisplatin, a drug used in cancer treatment

diuretics (water pills)

fluoride poisoning

Certain drugs may be less effective when taken with magnesium supplements. These include some antibiotics, and digoxin, a heart medication. Iron may be absorbed more poorly in the presence of magnesium.

Some minerals decrease the absorption of magnesium. These include calcium, manganese, and phosphate. Boron appears to increase magnesium levels.

No complications are expected from magnesium obtained from food and water. Potential complications related to excess use of magnesium supplements or from inadequate levels of magnesium are discussed above.

The safety of magnesium supplements in children has not been investigated. Breastfeeding women should avoid magnesium supplements and children should be encouraged to meet their magnesium requirements by eating a healthy diet high in green vegetables and whole grains and low in fat.

Learn More

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